A door exhibits physical properties which must be taken into account when providing a door system for a particular doorway. For example, a single swinging door panel will have a certain door edge velocity as a function of the width of the door. This is a factor which needs to be considered, for example, when ensuring that a person has exited the door swing path before causing the door to close. The width of the door panel also necessarily requires a predetermined operating envelope, which in turn determines the allowable proximity of other items to the door swing area. Furthermore, the door panel requires a certain operating kinetic energy to open. This is also a function of the width of the door and the mass of the door panel subassembly. As a result, it takes a certain minimum force to manually open such door panels in case of emergency, and in some cases, that force can be appreciable. Finally, if it is desired to use an automatic electro-mechanical door operator for this application, generally speaking, the larger the door, the more expensive the system components are likely to be. Also, the larger the door, the more susceptible it is to such environmental conditions as stack pressure (the pressure difference between ambient atmosphere, for example, and the air pressure of an interior space), and wind velocity.
If on the other hand it is proposed to use two doors with a center opening for a given doorway width to reduce edge speed, mass, door swing envelope, etc., problems arise if it is also proposed to operate both doors bi-directionally, especially automatically. Up to now, there has not been a satisfactory solution for synchronizing the bi-directional door swings of center-opening, bi-parting doors to open and close simultaneously through substantially equal angular distances so that a person may comfortably pass through the entire doorway in either direction, especially under automatic operation; nor has there been a solution in such situations for enabling a low-force, single-motion emergency breakout.